The present invention relates generally to spray nozzle assemblies, and more particularly, a to spray gun having a spray nozzle assembly at the discharge end and a reciprocatable valve needle for controlling liquid discharge from the spray nozzle assembly.
Spray guns having reciprocatably operated needle shut-off valves are well known in the art, such as shown in U.S. Pat. No. 5,707,010 assigned to the same assignee as the present application. The spray nozzle assembly of such spray guns includes an orifice defining member or insert, referred to herein as an orifice member, that defines the discharge orifice and a tapered valve seat for a reciprocatable control valve needle disposed in the liquid flow passageway for controlling the liquid flow through the spray nozzle assembly. The valve needle and tapered valve seat of the orifice member make metal contact during shut off, which concentrically locates and stops the valve needle and shuts off the liquid flow through the orifice member.
It is common to operate the control valve needle in predetermined relatively high speed cyclic movement for obtaining the desired spray discharge. To achieve reliable flow control and complete shut off during each operating cycle, it is necessary that the discharge orifice, valve seat, and control needle be manufactured with precision tolerances. Even then, manufacturing of such nozzle assemblies can result in quality control problems and costly parts rejection and reworking. For example, it is necessary that a tapered downstream end of the control valve needle concentrically and properly mate with the tapered valve seat. Surface imperfections in either the valve needle or seat can cause leakage problems and necessitate disassembly of the nozzle, lapping and reworking of the tapered valve seat surface, and polishing of the needle. Quality control and tolerance problems are compounded by reason of the relatively small sizes of the orifice member and valve needles used in such spray guns. Proposals to make the valve seat of a compliant material to more readily accommodate manufacturing variations have not been acceptable since a compliant material will not precisely stop and concentrically orient the valve needle as required and will deform during usage, causing even greater shut off problems.
Further problems can occur with spray nozzle assemblies of existing spray guns during field replacement of the orifice members. Typically the orifice member periodically is replaced in the field by reason of wear or the need to change the orifice size. While such orifice members are designed for easy replacement without the necessity for disassembling and replacement of the valve needle, even small amounts of wear on the needle can result in incomplete valve shut-off with the new orifice member. This can again necessitate reworking or polishing of the valve seat or needle to achieve proper shut off. When a number of nozzle assemblies must be maintained, as is common in many manufacturing operations, this can be particularly costly and time consuming.
Still a further problem with field maintenance of existing spray nozzle assemblies is inventory, in terms of the number of different models and sizes of orifices members, that must be offered by a manufacturer and stocked by the user. For example, such spray nozzle assemblies commonly have different sized needle valves, i.e., typically either 0.093 inches or 0.125 inches in diameter, and in order to minimize manufacturing and inventory requirements, it is desirable that replacement orifice members be replaced in the field for use with the different sized shut-off needles.
It is an object of the present invention to provide a spray gun or like spray device having a spray nozzle assembly with an orifice member adapted for more reliable shut off.
Another object is to provide a spray nozzle assembly as characterized above which can be economically manufactured with improved quality control.
A further object is to provide a spray nozzle assembly of the above kind which precisely and concentrically locates the valve needle and provides a reliable liquid seal while accommodating small tolerance variations and surface imperfections in the valve seat and needle.
Still another object is to provide a spray nozzle assembly of the foregoing type in which the orifice member is adapted for reliable use in spray guns or the like which have different sized valve needles.
Yet another object is to provide an orifice member for spray nozzle assemblies of the above kind that facilitates reliable field installation and replacement.
Still a further object is to provide a spray nozzle assembly with an orifice member of a design which minimizes inventory requirements.
Other objects and advantages of the invention will become apparent upon reading the following detailed description and upon reference to the drawings, in which: